The present invention relates generally to antenna systems for use in wireless communication systems. More particularly, the present invention relates to dual and multi-band antenna systems for use in wireless communication systems.
The expansion of mobile and personal cellular telephone systems has been rapid and widespread during the last few years. originally, cellular telephone systems were designed to provide communications services primarily to vehicles and thus replace mobile radio telecommunication systems. Advancements in technology and production have sufficiently decreased the costs of cellular service to the point at which cellular telephone service has now become affordable to a majority of the general population. Therefore, a "cellular telephone system" no longer strictly refers exclusively to cellular telephones, which originally were physically attached to and made a part of a vehicle. A cellular telephone system now includes portable, personal telephones which may be carried in a pocket or purse and which may be easily used inside or outside a vehicle or building.
Traditionally, wireless communication systems have included antenna systems which transmit and receive radio frequency ("RF") signals within the AMPS bands of frequencies in the United States or the GSM bands of frequencies in Europe. Wireless communication systems which operate in the AMPS or GSM frequency bands generally operate in a low frequency band. In the United States, the AMPS bandwidth used for cellular communication extends from about 824 Mhz to about 894 MHz. In Europe, the GSM bandwidth extends from about 890 MHz to about 960 MHz.
The wireless communications industry has recently broadened the scope of communications services by providing small, inexpensive, hand-held transceivers that transmit and receive voice and/or data communications, notwithstanding the geographic location of the user. This newer communications system operates at a higher frequency band than the AMPS/GSM frequency bands and has generally been referred to as a personal communication network/personal communication system ("PCN/PCS"). The PCN/PCS-type systems are envisioned to be wireless communication systems which should, for all intents and purposes, eliminate the need for separate telephone numbers for the home, office, pager, facsimile or car.
With the recent surge in the use of wireless communication devices, a need has grown to extend the capacity and to improve the communication quality and security of the applicable wireless communication system has also grown. As such, several countries and communication providers have agreed upon international communication standards and set aside a portion of the ultra-high frequency microwave radio spectrum as frequency bands which are dedicated exclusively for PCN/PCS communication systems.
On a worldwide basis, the PCN/PCS frequency band is expected to extend from about 1.5 GHz (1500 MHz) to about 2.4 GHz (2400 MHz). Within that band, individual countries have set aside particular portions of it for their respective PCN/PCS wireless communication systems. For example, Japan has set aside from about 1.49 GHz (1490 MHz) to about 1.521 GHz (1521 MHz), Europe has set aside from about 1.710 GHz (1710 MHz) to about 1.880 GHz (1880 MHz) and the United States has set aside from about 1.850 GHz (1850 MHz) to about 1.990 GHz (1990 MHz) for their PCN/PCS systems.
The bandwidths of the above different frequency bands represent approximately 11%, or only about 200 MHz, of the total possible bandwidth set aside for PCN/PCS-type wireless communication systems. The lowest frequency included within this PCN/PCS bandwidth is almost two times higher than the standard frequency of around 800 MHz at which cellular telephone communication systems operate within the United States. As a general rule, one can consider the conventional wireless communication frequency bands and the intended PCN/PCS frequency bands to be separated by just about 1000 MHz.
While operating within the PCN/PCS frequency bands, wireless communication systems typically employ principles of digital communication that have improved the communication quality and strengthened their security of the PCN/PCS over the conventional cellular telephone systems which utilize the lower frequency bands.
An ever increasing number of regions within the United States now utilize the PCS frequency bands for wireless communications, while in Europe, the use of PCN frequency bands is growing. In most of these regions, wireless telephone units must be able to operate in both the higher and lower bands of frequency (i.e., in both the AMPS and PCS frequency bands in the United States; in both the GSM and PCN frequency bands in Europe) so that a user of such units may selectively choose the frequency band of operation for the unit. Additionally, the units themselves may selectively choose their frequency band of operation so that the chosen band matches the frequency band of the electromagnetic signals received from a wireless telephone unit placing an incoming call to that particular unit.
Under these circumstances, it is desirable to develop antenna systems that are tuned to resonate within both of the above-identified bands of frequency (i.e., the AMPS and PCS bands for United States-based wireless communication systems and the GSM and PCN bands for European-based wireless communication systems). One approach would be to use a dual port antenna system utilizing two radiators with each radiator being tuned to resonate within a different frequency band. Although theoretically feasible, as a practical matter, this type of antenna systems is undesirable because it would be larger than a single radiator system. Furthermore, such an antenna system would require two RF signal feed lines resulting in a system more expensive to manufacture, thereby increasing the ultimate cost to the consuming public.
In light of these disadvantages, there is a present need for a single port, dual band antenna that is tuned to resonate within both bands of frequency in the user's region, i.e., in both the AMPS and PCS frequency bands in the United States and in both the GSM and PCN frequency bands in Europe.
One dual band antenna system generally available in the prior art uses the structure of a monopole antenna modified for dual band operation. Broadband monopole antennas are widely used in the mobile antenna design industry because of their simple embedding characteristics, their solid mechanical features and their inherent advantages over a ground plane environment. However, it is believed that some dual band antenna systems utilizing monopole radiators would be unable to maintain the simple structure of a standard broadband monopole antenna and/or obtain the minimum level of efficiency within both of the resonant bands of frequency necessary for commercially marketable quality of the product. Design modifications that would be necessary to allow those antenna systems to operate have raised the complexity of the systems as well as their cost.
Further, dual band antenna systems utilizing monopole radiators are typically mounted externally on the vehicle so that the monopole radiator is exposed to the external environment, which may lead to a shorter life and less efficient performance due to the environment. Finally, dual band, monopole radiator antenna systems are undesirable because they are not low profile. Accordingly, as a practical matter, dual band, monopole radiator antenna systems are not a feasible solution to the above-identified dilemma.
The second type of prior art dual band antenna systems are antenna systems that utilize two microstrip antennas. These are not typically single port, dual band antennas, but are rather dual port, dual band antenna systems. These systems have a major disadvantage in that they need an additional RF signal feed line. Furthermore, the operation of microstrip antenna dual band antenna systems depends upon the use of a ground plane. If a ground plane is not included or cannot be used in the system, the antenna will not operate.
The standard microstrip antenna configuration comprises two conductive layers of material separated by a passive substrate such as a printed circuit board. One conductive layer serves as the radiator portion of the antenna while the other conductive layer serves as a ground plane. This inherent need for a ground plane by all microstrip antennas makes them less desirable than the ground plane independent antenna of the present invention.
Still, dual band antenna systems that utilize microstrip antennas are classified as directional antennas since the electromagnetic signals are transmitted from and received by the antenna in a single direction, usually from the radiator portion of the antenna away from its associated ground plane.
A third prior art dual band antenna system utilizes a monopole type radiator connected to an external coupling element that is capacitively coupled with an internal coupling element. The internal coupling element is, in turn, connected to the transceiver by an RF signal feed line. These antenna systems may be glass mounted but their use has revealed a considerable number of disadvantages. In particular, such glass mount antennas utilize two modules mounted on respective outside and inside surfaces of a window in order to transmit signals between the opposing modules through the window glass. In these capacitively coupled antenna systems, two metal plates are used in the modules which cooperatively act as a capacitor to transmit RF energy through the intervening dielectric window glass.
These glass mount capacitive coupling-type antenna systems are also disadvantageous because they require a ground plane. Most glass mount surroundings cannot provide an ideal ground plane for the monopole radiator section of the antenna system, thereby degrading its performance. Furthermore, the physical characteristics of the dielectric to which the antenna is mounted, i.e., the window, generally inhibit sufficient capacitive coupling between the two coupling elements in both of the desired frequency bands. As such, loss occurs in the prior art glass mount antennas because they must propagate RF signals through the dielectric material and must further match the impedance of the external monopole type radiator.
Finally, the monopole type radiator used in these coupled dual band antenna systems is also mounted externally on a vehicle so that these systems are susceptible to the previously described disadvantages which result from exposure of portions of an antenna system to the outside environment.
In light of the aforementioned shortcomings of the available dual band antenna systems, it is desirable to provide a dual band antenna system comprising a low profile, ground independent, omni-directional, dual band antenna which may be mounted to the surface of a dielectric. Accordingly, the present invention is directed to an antenna system that overcomes the aforementioned shortcomings of the prior art and which utilizes novel radiating elements to provide a ground plane independent, dual band antenna suitable for transmission and reception of signals in two separate, selected frequency bands in either of the AMPS/GSM and either of the PCN/PCS frequency bands.
It is therefore a general object of the present invention to provide a new dual band antenna system that is ground plane independent.
It is another object of the present invention to provide an inexpensive dual band antenna system that includes a low-profile, omni-directional antenna.
It is yet another object of the present invention to provide an improved antenna system having a dual band, ground plane independent concealed antenna that is adapted for mounting on a glass surface of a vehicle or building, the antenna assembly having a flexible housing that adapts to its mounting surface.
It is still yet another object of the present invention to provide a dual band antenna system which includes a planar radiating structure formed on a circuit board that utilizes both broadband and microwave technology to transmit and receive RF signals at two separate, selected frequency bands in either of the AMPS/GSM frequency bands and either of the PCS/PCN frequency bands.
It is yet another object of the present invention to provide a flexible outer housing for an antenna assembly having a discontinuous outer configuration that permits the housing to conform to the shape of different dielectric surfaces, to thereby facilitate the installation of the antenna assembly.
It is yet a further object of the present invention to provide a ground-plane independent, dual band antenna system that utilizes a radiating structure having a tuning bridge that capacitively and inductively loads a portion of the radiating structure to thereby permit selection of two different resonant frequency bands for the antenna system.
It is still another object of the present invention to provide a dual band antenna system having a tuning bridge which permits selection of the two resonant frequency bands of the antenna system by setting the electrical length and/or width of the elements of the tuning bridge to specific values.
It is yet another object of the present invention to provide a dual band antenna system comprising a tuning bridge formed with transmission line-like conductive strips.